Lumen

The term [lumen] is Latin and means "light". It is an international measure of light intensity. The plural form is either [lumens] or the Latin version [lumina].

The question is how did this term end up meaning the "internal opening or cavity of a hollow organ"? Dr. J. Dirckx (1976) explains that the term [lumen] in gastrointestinal anatomy was not used until the late 19th century, but it was initially used by microscopists looking at cross sections of small vessels. Since the empty interior of the vessel was represented on the histological slide as a clear, lighted region, they started calling that the "light" of the vessel, or [lumen].

The root term for [lumen] is [-lumin-] and can be found in over 30 words in English and related to light, such as luminosity, luminaria, luminescent, luminous, illumination,  illuminator, intraluminal, transluminal, endoluminal, etc.

The correct adjective form for [lumen] is [luminal], as stated by Haubrich (1997). The point is that the use of the term "lumenal" as an adjective form for lumen is not correct. This term can be seen in many textbooks today. The proper form for the NOTES acronym should be "Natural Orifice Transluminal Endoscopic Surgery" and not "translumenal". 

See how you can "illuminate" this article by hovering your cursor over the light bulb!

Sources:
1. "The Language of Medicine" John H. Dirckx Pub: Harper & Row 1976
2. "Medical Meanings" Haubrich, William S. Am Coll Phys Philadelphia 1997
3. "The origin of Medical Terms" Skinner, AH, 1970